find命令如何搜索文件 [英] How does the find command search for files

问题描述

从另一个线程中查询移动文件已经老化了x分钟，这个问题出现了:

Quarrying out from another thread Move file that has aged x minutes, this question came up:

通常在Linux中找到的find命令如何在当前目录中搜索文件?

How does the find command found typically in Linux search for files in the current directory?

考虑一个包含大量文件的目录，然后:

Consider a directory that contains a fairly large amount of files, then:

首先find MY_FILE.txt立即返回，然后find . -name MY_FILE.txt需要更长的时间.

Firstly find MY_FILE.txt returns immediately and secondly find . -name MY_FILE.txt takes much longer.

我使用strace -c来查看这两种情况的发生，并且我了解到第二个命令调用了目录扫描，这解释了为什么它比较慢.

I used strace -c to see what happens for both and I learned that the second command invokes a directory scan, which explains why it's slower.

因此，必须对第一个命令进行优化.谁能指出我合适的资源或快速解释如何实现?

So, the first command must be optimized. Can anybody point me to the appropriate resource or provide a quick explanation how this might be implemented?

推荐答案

find的语法为find <paths> <expression>，其中 paths 是开始搜索的文件和目录的列表.从这些位置开始查找，然后递归(如果它们是目录).

The syntax for find is find <paths> <expression>, where paths is a list of files and directories to start the search from. find starts from those locations and then recurses (if they're directories).

编写find . -name MY_FILE.txt时，它将在./目录下执行递归搜索.但是，如果您编写find MY_FILE.txt，则是告诉它在./MY_FILE.txt处开始搜索，所以它会这样做:

When you write find . -name MY_FILE.txt it performs a recursive search under the ./ directory. But if you write find MY_FILE.txt then you're telling it to start the search at ./MY_FILE.txt, and so it does:

$ strace -e file find MY_FILE.txt
...
newfstatat(AT_FDCWD, "MY_FILE.txt", 0x556688ecdc68, AT_SYMLINK_NOFOLLOW) = -1 ENOENT (No such file or directory)
...
(No such file or directory)
: No such file or directory
+++ exited with 1 +++

由于该路径不存在，因此只需一个系统调用即可确定不存在此类文件.它调用newfstat()，得到一个No such file or directory错误，就是这样.

Since the path doesn't exist, it only takes a single system call to determine that there's no such file. It calls newfstat(), gets a No such file or directory error, and that's that.

换句话说，find MY_FILE.txt不等同于find . -name MY_FILE.txt.哎呀，因为您不要求它进行搜索，我什至认为它没有用.您只是要求它告诉您MY_FILE.txt在当前目录中是否存在.但是您只需调用ls MY_FILE.txt就能找到答案.

In other words, find MY_FILE.txt isn't equivalent to find . -name MY_FILE.txt. Heck, I wouldn't even call it useful because you're not asking it to search. You're just asking it to tell you if MY_FILE.txt exists in the current directory or not. But you could find that out by simply calling ls MY_FILE.txt.

区别在于:

[~]$ cd /usr
[/usr]$ find . -name sha384sum
./bin/sha384sum
[/usr]$ find sha384sum
find: ‘sha384sum’: No such file or directory

第一个执行递归搜索并找到/usr/bin/sha384sum.第二个不递归并立即失败，因为/usr/sha384sum不存在.它看起来没有更深.这是在一纳秒内完成的.

The first one performs a recursive search and finds /usr/bin/sha384sum. The second one doesn't recurse and immediately fails bcause /usr/sha384sum doesn't exist. It doesn't look any deeper. It's done in a nanosecond.

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